1. Field of the Invention
The present invention is directed generally to an apparatus for affixing wires or wire ribbons to terminal elements, and more particularly to an apparatus having touch-down or pressure electrodes for producing wire bridges.
2. Description of the Related Art
An apparatus for micro-welding using a split electrode is disclosed in the periodical "Feinwerktechnik", volume 75, 1971, pages 201-206. A repair method is described which eliminates errors occasionally occurring in the manufacture of electrical printed circuit boards. Such errors lead to inadmissibly constricted or interrupted interconnects. When the error locations are recognized, then gold-plated fine ribbons of nickel or fine ribbons of copper are placed over and metallically connected to the interconnects. Since the electrical printed circuit boards are subjected to a soldering process after being equipped with component parts, the repair of the interconnects is performed with micro-resistance welding so that the repair locations do not suffer damage do to temperatures occurring durring soldering and so that the connections do not undo again.
In the periodical "Feinwerktechnik", Volume 73, 1969, pages 209-216, an article investigates the influencing quantities occurring during micro-resistance spot welding of copper and nickel ribbons. A welding head disclosed therein is designed so that welding can be carried out not only with a direct electrode arrangement but also with an indirect electrode arrangement. Resistance spot welding with an indirect, parallel electrode arrangement, also referred to as gap welding, is especially well suited for contacting miniature component parts. The spacing of the indirectly arranged electrodes, which are also frequently referred to as touch-down or pressure electrodes, amounts up to 1 mm. The electrodes are connected to the electrode arm independently of one another by springs. This compensates for irregularities in the workpiece surface and guarantees approximately uniform surface pressure between the electrodes and the workpiece.
During the manufacture of motor vehicle ignition devices, wire bridges must frequently be welded in between the housing terminal lugs and the allocated terminals of ceramic thick-film substrates. The maximum height difference of the individual connection points amounts to approximately 50 mm. Thus, an oblique placement of the wire bridges and a vibration-proof connection with high mechanical and thermal loadability are required. Up to now, such wire bridges were produced by boss welding of flexible portions of thin sheets or by resistance welding of pre-bent, discrete wire sections in accordance with German published application No. 32 33 225.